The following is offered as background information only and is not admitted to be prior art to the present invention.
Growth factor receptors are cell-surface proteins. When bound by a growth factor ligand, growth factor receptors are converted to an active form which interacts with proteins on the inner surface of a cell membrane. This leads to phosphorylation on tyrosine residues of the receptor and other proteins and to the formation inside the cell of complexes with a variety of cytoplasmic signaling molecules that, in turn, affect numerous cellular responses such as cell division (proliferation), cell differentiation, cell growth, expression of metabolic effects to the extracellular micro environment, etc. For a more complete discussion, see Schlessinger and Ullrich, Neuron. 9:303-391 (1992) which is incorporated by reference, including any drawings, as if fully set forth herein.
Growth factor receptors with PTK activity, known as receptor tyrosine kinases ("RTKs"), comprise a large family of transmembrane receptors with diverse biological activity. At present, at least nineteen (19) distinct subfamilies of RTKs have been identified. An example of these is the subfamily designated the "HER" RTKs, which include EGFR (epithelial growth factor receptor), HER2, HER3 and HER4. These RTKs consist of an extracellular glycosylated ligand binding domain, a transmembrane domain and an intracellular cytoplasmic catalytic domain that can phosphorylate tyrosine residues on proteins.
Another RTK subfamily consists of insulin receptor (IR), insulin-like growth factor I receptor (IGF-1R) and the insulin receptor related receptor (IRR). IR and IGF-1R interact with insulin, IGF-I and IGF-II to form a heterotetramer of two entirely extracellular glycosylated a subunits and two .beta. subunits which cross the cell membrane and which contain the tyrosine kinase domain.
A third RTK subfamily is referred to as the platelet derived growth factor receptor ("PDGFR") group, which includes PDGFR.alpha., PDGFR.beta., CSFIR, c-kit and c-fms. These receptors consist of glycosylated extracellular domains composed of variable numbers of immunoglobin-like loops and an intracellular domain wherein the tyrosine kinase domains is interrupted by unrelated amino acid sequences.
Another group which, because of its similarity to the PDGFR subfamily, is sometimes subsumed in the later group is the fetus liver kinase ("flk") receptor subfamily. This group is believed to be made of up of kinase insert domain-receptor fetal liver kinase-1 (KDR/FLK-1), flk-1R, flk-4 and fms-like tyrosine kinase 1 (flt-1).
One further member of the tyrosine kinase growth factor receptor family is the group known as the fibroblast growth factor ("FGF")receptors. This group consists of four receptors, FGFR1-4, and seven ligands, FGF1-7. While not yet well defined, it appears that the receptors consist of a glycosylated extracellular domain containing a variable number of immunoglobin-like loops and an intracellular domain in which the PTK sequence is interrupted by regions of unrelated amino acid sequences.
A more complete listing of the known RTK subfamilies is described in Plowman et al., DN&P, 7(6):334-339 (1994) which is incorporated by reference, including any drawings, as if fully set forth herein.
In addition to the RTKs, there also exists a family of entirely intracellular PTKs called "non-receptor tyrosine kinases" or "cellular tyrosine kinases". This latter designation, abbreviated "CTK", will be used in this disclosure. CTKs do not contain extracellular and transmembrane domains. At present, over 24 CTKs in 11 subfamilies (Src, Frk, Btk, Csk, Abl, Zap70, Fes, Fps, Fak, Jak and Ack) have been identified. The Src subfamily appear so far to be the largest group of CTKs and includes Src, Yes, Fyn, Lyn, Lck, Blk, Hck, Fgr and Yrk. For a more detailed discussion of CTKs, see Bolen, Oncogene, 8:2025-2031 (1993), which is incorporated by reference, including any drawings, as if fully set forth herein.
Both RTKs and CTKs have been implicated in a host of pathogenic conditions including, significantly, cancer. Others include, without limitation, psoriasis, hepatic cirrhosis, diabetes, atherosclerosis, angiogenesis and a variety of renal disorders.
With regard to cancer, two of the major hypotheses advanced to explain the excessive cellular proliferation that drives tumor development relate to functions known to be PTK regulated. That is, it has been suggested that malignant cell growth results from a breakdown in the mechanisms that control cell division and/or differentiation. It has been shown that the protein products of a number of proto-oncogeries are involved in the signal transduction pathways that regulate cell growth and differentiation. These protein products of proto-oncogenes include the extracellular growth factors, transmembrane growth factor PTK receptors (RTKs) and cytoplasmic PTKs (CTKs), discussed above.
In view of the apparent link between PTK-related cellular activities and a number of human disorders, it is no surprise that a great deal of effort is being expended in an attempt to identify ways to modulate PTK activity. Some of these have involved biomimetic approaches using large molecules patterned on those involved in the actual cellular processes; e.g., mutant ligands (U.S. Pat. No. 4,966,849); soluble receptors and antibodies (App. No. WO 94/10202, Kendall and Thomas, Proc. Nat'l Acad. Sci., 90:10705-09 (1994), Kim, et al., Nature, 362:841-844 (1993)); RNA ligands (Jelinek, et al., Biochemistry, 33:10450-56); Takano, et al., Mol. Bio. Cell 4:358A (1993); Kinsella, et al., Exp. Cell Res. 199:56-62 (1992); Wright, et al., J. Cellular Phys., 152:448-57)) and tyrosine kinase inhibitors (WO 94/03427; WO 92/21660; WO 91/15495; WO 94/14808; U.S. Pat. No. 5,330,992; Mariani, et al., Proc. Am. Assoc. Cancer Res., 35:2268 (1994)).
More recently, attempts have been made to identify small molecules which act as PTK inhibitors. For example, bismonocylic, bicyclic and heterocyclic aryl compounds (PCT WO 92/20642), vinylene-azaindole derivatives (PCT WO 94/14808) and 1-cyclopropyl-4-pyridylquinolones (U.S. Pat. No. 5,330,992) have been described as tyrosine kinase inhibitors. Styryl compounds (U.S. Pat. No. 5,217,999), styryl-substituted pyridyl compounds (U.S. Pat. No. 5,302,606), quinazoline derivatives (EP App. No. 0 566 266 A1), selenaindoles and selenides (PCT WO 94/03427), tricyclic polyhydroxylic compounds (PCT WO 92/21660) and benzylphosphonic acid compounds (PCT WO 91/15495) have all been described as PTK inhibitors with potential utility for the treatment of cancer.
An area in need of improvement with regard to PTK-active compounds is their bioavailability in vivo. It is not uncommon for a molecule to exhibit good PTK modulating activity in vitro, where it can be placed in immediate proximity to the PTK of interest, but to have substantially less, sometimes no, activity in vivo. Without being bound to a particular theory, applicants believe that this phenomenon may be due to the fact that many molecules of interest as modulators of PTK activity, including indolinones, tend to be lipophilic. However, in many cases, the region where the PTKs reside and perform their function are aqueous in nature. Thus, the compounds might not be capable of reaching the active site. Improving the hydrosolubility of indolinones could lead to compounds with improved bioavailiabilty and thereby improved PTK modulation in vivo.